In certain, well-hidden locations within the southern seas, giant clams are cultivated for their pearls of immense size. The clams are kept in relatively shallow water, typically where a significant river dumps into the sea. Locations are chosen for nearby reefs which make approach by ships dangerous, a hedge against pirate raids. The farmers row smaller boats out to the clam beds and dive down to harvest the pearls. This requires a strenuous battle with the clam to pry it open.
Gogglers are known to tend to their own clam beds, often in deeper water. The size and quality of these pearls equal the higher risk in obtaining them.